Title:  An Architecture for Broadband Internet Services over a WDM-based 
	Optical Access Network

By:  Eytan Modiano and Eric Swanson, MIT Lincoln Laboratory

	We describe a WDM-based access network architecture for
providing internet services.  The access network refers to the portion
of the communication infrastructure responsible for reaching the
customer premises.  Because of the proximity to the end-user, an
access network is quite different from a backbone network and hence
offers additional technology and economic challenges.  The relatively
low-rate individual traffic flows need to be multiplexed into the
higher- rate backbone trunks, thus requiring multiplexing and grooming
equipment.  In addition, the data traffic is quite bursty because it
has not yet been sufficiently aggregated and could therefore benefit
from statistical multiplexing.  Complicating matters further,
equipment must be cheaper in the access network than in the backbone
or interoffice networks because equipment is shared over a smaller set
of customers.
	WDM technology has emerged as the foremost solution to
high-speed transmission and is beginning to dramatically change the
underlying characteristics of backbone networks.  While WDM is likely
to soon dominate the backbone, architectural advancements in the
access environment have not kept pace with that of the network core,
preventing Internet users from fully realizing the potential benefits
and huge capacity of the optical technology.
	Our architecture uses a low cost passive optical collection
and distribution network for connecting the end-users to an access
node, and a configurable optical Feeder network (e.g., WDM rings) for
connecting the different access nodes to each other and to a backbone
network.  We will discuss issues and mechanisms that would allow
internet protocols to take advantage of the huge bandwidth and
configurability of WDM. Some of the issues involved include: the
choice of electronic multiplexing and switching between the IP and WDM
layers; modifications of IP to interface with WDM in order to make use
of new optical layer services; network reconfiguration algorithms that
improve network capacity by altering the network logical topology in
response to changes in traffic conditions; traffic grooming algorithms
to minimize electronic costs at access nodes and to make efficient use
of wavelengths in the Feeder; and scaleable protocols for efficient
channel access such as optical-layer MAC protocols for
Bandwidth-on-Demand services in passive C/D networks.
	We will also consider the impact of this new, high capacity,
reconfigurable WDM layer of higher layer protocols.  For example, we
will discuss the interaction of TCP flow control with the underlying
WDM-based network; the impact of rapid topology reconfiguration on IP
route calculations and the potential for routing table instabilities;
and extending multi-layer switching into the optical domain.